5/18/97 IA chase by Gilbert Sebenste


From: "Gilbert L. Sebenste" (sebenste@geog.niu.edu)
Subject: Chase summary, 5/18/97: You DO make me smile, Iowa!

Hello chasers,

As Roger Edwards might say, open up the Rand McNally, open a cold (diet)
Dr. Pepper, and get ready for a cool cyberchase!

Friday afternoon, May 16. Forecast soundings from the AVN and the 48 hour
NGM/ETA confirm that something might happen on Sunday. But as the 12Z
models for Saturday, May 17th roll in, it looks good. Not super, but it
goes like this:

A surface low coming down from southwest Canada is forecast to move across
southern MN and WI by 0Z Monday. At that point, in the warm sector across
IL, models are disagreeing about how much moisture will be present, and
how warm it will get into the warm sector. But first things first: will
an overnight MCS destroy the chances for surface heating the next day? And
will the best activity be along the warm front?

The latter scenario is dismissed. Clouds will make it *way* too cool, as
lots of isentropic lift will take the available moisture and give
widespread general rain and weak thunderstorms ahead of the warm
front. So, I turn my attention to the warm sector.

With the surface low continuing to deepen as it spins up, pressure falls
should back the winds more. The NGM says it will only be in the 70's in
the warm sector, while the ETA heads for a much more robust upper 80's.
But the NGM goes for upper 60 dewpoints and the ETA goes for right around
60. This will be critical to figure out. As I pull up the 18Z Saturday
surface map, I notice a classic low level jet situation setting up, with
dewpoints to the IA/MO border already in the low 60's, with upper 60's not
far behind. And already the NGM is out to lunch on temperatures. Unless a
huge MCS occurs, which is not likely, moisture advection will be plenty
and TD's should make it into the upper 60's in IL, with temps in the upper
80's. That brings CAPE to 4000 J/KG with 500 MB temps at -13. With 10C 700
MB temps advecting in from the south, things will be capped until the
shortwave trough helps kick things off late in the afternoon. Speed shear
is good, directional shear is adequate but not great, and it appears any
supercells that do develop will be borderline classic/HPs. This forecast,
as it turns out, will be dead on except for one thing. My call is northern
IL for a chase. But that will change.

10AM (15Z) Sunday. I drag my rear out of bed and head for the NIU weather
office. Our machine, taiga, is nearly hosed due to web server problems. I
install a new version of WXP for THE STORM MACHINE which corrects that.
But then our data feed from the Internet goes down, and I have to make
some quick decisions on how to fix that. After I get all the software
problems fixed, I have wasted precious time--almost an hour getting
everything back online.

Unfortunately, problems with NIU's DiFAX data vendor mean I have no maps,
and Purdue is not updating for some reason. Arrrgh. Finally, with our
backup data feed in place, I make an Iowa mesonet and midwest surface map
on WXP shortly after 11AM, print it out, and go to work.

Right away, I see trouble. The pre-frontal trough is still west of Des
Moines, and the cold front is just getting to Omaha. Also, overnight
convection from the warm front has left a distinct outflow boundary from
Sterling, IL (SQI) to Moline to Iowa City (IOW) and then west-southwest
north of Lamoni (30I). Eastern Iowa has cleared out and my jaw is
dropping. Already temps are in the low 80's, with mid-60 dewpoints and 70
TD's not far away. Then the phone starts ringing off the hook. George
Sreckov, a recent graduate, and Ryan Williams want to go chasing. Get in
here fast, boys! Ryan Towell calls and offers to hold down the NIU weather
office and watch satellite, radar and surface data while we chase. That's
nice, and then people start coming in. George can't make it until 2 PM
(arrgh), but that's OK. I figure the cap will hold until 3 PM before
things start breaking loose. Iowa City is my target town. That too would
verify nicely, but not for us.

By 19Z (2 PM CDT) everyone is ready to go. I hold off for just a few
minutes to get a quick look at the 19Z surface data from the Iowa mesonet.
Amazing. In the warm sector, cu's are popping along the outflow boundary,
and the shortwave is clearly visible west of Des Moines near Omaha. A
tornado watch is issued for central and eastern IA until 2Z MOnday (9PM
Sunday), and we are GONE! I savor the 90 degree (32C) temperatures and 70
degree (21C) dewpoints in eastern and southern IA with south winds at 20
knots gusting 30!!!!!

After packing our two-way radios, road maps and such, at 2:15 PM we leave
NIU and head for I-88 west. We learn that David Paul, another recent
graduate who lives in Carroll County about 60 miles west near I-88 wants
to join us. He has a cell phone (we have 4!), so we'll meet him at State
Road (SR) 78 west of Sterling. We meet Dave around 3 PM and he's talking
with Ryan back at NIU. Since he gets free weekend calling on his cell
phone, he can take his time getting all the info. A severe storm has now
popped up west of Cedar Rapids, moving east. That's what we want to hear!
The cap has broken and the storm is growing explosively, feeding on the
high theta-e air. We get on I-88 and the caravan of 3 cars speeds towards
IA, with the remake of "I can see clearly now, it's going to be a bright
sunshiney day!" blaring on our radio.

We get on I-80 west in the Quad Cities and hit the Mississippi river at
3:49PM. We tune our radios to WMT-AM 600 out of Cedar Rapids, which has in
the past offered me good severe weather coverage. But before this day is
over, I will hear one of the finest radio broadcasts of severe weather
coverage I've ever heard. An old-time music program ("big band") is
swinging to Jimmy Dorsey and Frank Sinatra, and our chase team who like to
thrive on Megadeth, Aerosmith, Hootie and the Blowfish and Garth Brooks
don't seemed to be to thrilled about listening to this. But then they
break in and announce a severe thunderstorm warning for Benton and Lynn
counties, with even a few funnel clouds reported in central Benton county!
Suddenly, Paul Anka doesn't sound so bad!

We decide to pull over at the rest stop west of Davenport to check out the
radar, and make a quick pit stop. As we pull in at 3:52PM, KGAN-TV's
meteorologist break in with a tornado warning for Lynn county, with a
tornado on the ground 11 miles northwest of Cedar Rapids! Still going 20
MPH in the rest area, getting close to the main building, I grab the radio
and simply say "Abort pitstop!". Paul doesn't have a radio in his car, so
I motion to him to keep going. I decide that US 61 at Davenport north to
Grand Mound will be the way to go. At 4:05PM, we get of I-88 and head
north on US-61. We make a quick pit stop at an Amoco just down the road
from the NWS office, with the WSR-88D radome looming over the gas station
and the trees. With full gas tanks and certain critical body parts empty,
we head back north on 61 as other touchdowns come in to the radio station!

At 4:20PM, we decide to head west on 30, hoping the storms will turn
right. We now hear of ANOTHER supercell south of the main one at Cedar
Rapids, heading towards our location. That's what we want! We continue
west on 30, and at 4:32PM we are 4 miles east of Wheatland. A few minutes
later, we hear of a tornado on the ground 20 miles west near
Mechanicsville right on US 30 as we cross the Wapsipinicon river!
At 4:42, Dave advises us he has a graduation party to go to, and he has to
terminate the chase. Oh, man. That stinks. We say goodbye to him via
cell phone as we watch him turn around. As we look west, the sky is black.
Frequent lightning is now flashing off to our west and northwest. At
4:43 PM, we hit Lowden, and at 4:45 PM we are 2 miles west of Lowden. As
we break into an open are with a clear view to our west and northwest, we
can see a low contrast but HUGE rotating wall cloud off to our
northwest!!!

This thing is a beast. It looks like a barrel in the sky. The base of the
wall cloud is very low. It appears something is trying to happen, but the
contrast isn't good, with hazy skies. Still, it is adequate to see all the
features we need...including an oncoming train which paralells the
west-east road to our north, and blocks our view!!! ARRRRGH!!!! It is one
of the longer trains I have seen (it went all the way back to Lowden, so
it's almost two miles long), and he's only doing 40 MPH or so. We hear of
more touchdowns (DOUBLE ARRRGH!), and through the breaks in each car a few
people think they see a funnel develop. Great. If we miss this one because
of a train...

4 long minutes later, at 4:52PM, the train passes and the wall cloud is
becoming detatched. That's not good, and we watch it for a few more
minutes before I decide we better get east of the storm to watch it.
At 4:56 PM we head one mile east (which is one mile west of Lowden) on US
30 and turn north on a gravel road to get closer. at 5PM we stop on this
road one mile north of US 30. At 5:01 PM a new wall cloud develops...near
the core of the storm. Dang. This is evolving into an HP. But we can't see
very well because a hill is in the way. We drive to the crest of the hill
and find a FANTASTIC high point view of the entire storm. Excellent!
Then, a startling sight: A news helicopter is flying near the HP core,
fading a little from time to time in the rain. We look incrediculously
at this nut, and the comments fly: "Hey guys, keep your cameras on the
helicopter...when it gets hit by lightning, you'll have great video for
CNN!". Good gravy, this pilot was a few french fries short of a Happy
Meal! As we watch, we seem to see something in the storm where the meso
is, but we aren't sure of what. Video shows a white cone to the ground,
faint, but it's there. The problem is that I can't tell if that's a weird
hail shaft or a nice looking tornado. I don't count it as such, but then
we hear numerous spotters northeast of it saying they have a cone tornado
all the way to the ground. It was confirmed, but I still won't call it
such for us until I have others look at our tape.

At 5:04 PM we head back to U.S. 30 to head east and keep up with it. At
5:07 PM, a fairly low contrast, but definitely visible HP wall coud
reveals itself as we continue east just west of Lowden. In-cloud and
cloud to ground lightning is becoming very frequent with powerful
bolts in and around the mesocyclone. At 5:08 PM, we're in Lowden, and one
minute later after we pass through a no-doubt-about-it funnel cloud
descends from the north side of the mesocyclone. Here we go!!! But, it
does not touch down, and as we continue east at 5:13PM, the meso once
again becomes completely wrapped in rain. Dang it!

At 5:16PM we cross the Wapsipinicon river again, losing sight of the
storm. But at 5:18PM we reach Calamus, and head north on county road Y44,
where the meso slowly re-appears to our northeast! We fly north when
suddenly, the cell phone rings. It's Dave, and as he was heading back, he
heard about the additional tornado touchdowns and huge inflow jets of dust
racing into the low levels of the storm and decided "the heck with it!".
He called his folks and told them he will be a little late for the party.
He's just ahead of us, and we head east on county road E-63 at 5:22 PM.

As we watch, I notice something that disturbs me: A shower has formed just
southeast of the storm, and a line of showers extends southward from
there. I grimly announce on the two-way radio that "If it doesn't go in
the next 15 minutes, it won't".

Sure enough, no more than 10 minutes later, at 5:32PM, the storm clearly
is becoming outflow dominated, and it joins the developing squall line.
After hearing WMT's coverage, there are now two squall lines, with now
little hope of a supercell developing that we could catch. At 5:43 PM, we
reach Charlotte, and as we pass through the town, I say to myself "Man,
this town has a weed problem; look at all those white flowers" (yeah, I
don't know the name of them, after dandelions seed). But as we slow down,
I gasp: Golfball hail! We pull over and get some classic shots of everyone
holding the stones in their hand. The KGAN/WMT radio crew tells us
that the NWS has a warning for this and since they know about it, a
report from us wasn't necessary.

We head south into Clinton for dinner. Suddenly, a severe storm forms
right on top of us in a matter of minutes. Marble hail starts falling
and our drivers nearly panic. They race through the town trying to find
a gas station with a cover. My attempts to calm the drivers are futile as
visions of their mothers killing them for driving their new cars into
large hail completely block out any mental input from me. We screech
around corners in the blinding rain and hail. Finally, with no gas
stations to be found and in desperation, we drive under roadside trees
which provide sufficent coverage to stop the stones from damaging the
cars. After about 5 harrowing minutes, the storm moves east.

At 6:30PM the frazzled chase crew pulls into a Hardees to have dinner in
Morrison, IL. We hear about the supercell at Iowa city dropping golfball
hail on the hapless town for 15 minutes, and the tornado west of town as
well. It produces funnels, rotating wall clouds and a tornado at
Bettendorf around 7:30PM, but it is too far away to chase it...and it's
also getting too dark. We head home after eating, hitting NIU at about
9PM.

All in all, a very good chase! Maybe we did get a tornado on camera, but I
may never know. Still, everyone went away very happy, except for poor
Ryan, manning the consoles back at NIU, who suddenly got the itch to chase
when we saw the funnel clouds back in Iowa! :-)

Special thanks to: Ryan Williams, driver; Ed Boik, riding shotgun and
doing video (and thanks for the cell phones guys!); George Sreckov, driver
of car two and his team, and David Paul who called numerous times to keep
us updated minute by minute on what Ryan was seeing on radar. Big
thank you to Ryan Towell and Kevillee Potts manning radar at NIU; nice job
to WMT-AM 600 and KGAN-TV 2 for wall-to-wall coverage for two hours
(except for 15 minutes when the storm blew out their microphones and
record players; they went dark for 10 minutes and then played financial
news off of a satellite feed until the techies could get things working
again), and NWS DVN, who had timely warnings on everything!

Gilbert

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Gilbert Sebenste                                                     ********
Internet: sebenste@geog.niu.edu    (My opinions only!)                 *****
Owner of the Storm Chaser Homepage/SCH Canada                           ***
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